(1) A strategy of using a virus's own signal sequence to deliver antiviral peptides into cells has been tested. A cell-impermeable peptide inhibitor of herpes simplex virus (HSV) ribonucleotide reductase, when conjugated to a signal sequence from the envelope protein of HSV, was able to inhibit the growth of HSV in Vero cells. The carrier seems to show some specificity. It was capable of entering HeLa cells known to be infectable by HSV, but not MOLT-3 cells, a T-cell leukemia cell not infectable by HSV. (2) The partial amino acid sequence of a magnesium-dependent, calcium- inhibitable protein phosphatase (MCPP) revealed that it contained a 24- residue segment that is homologous to a region found in 12 other magnesium-dependent phosphatases. Also, the sequence contained an acidic region, which showed significant homology with a human leukemogenic protein called DEK. MCPP may be a nuclear protein regulating DEK and SET, another leukemogenic protein known to serve as substrate for MCPP. (3) Immunoprecipitation studies confirmed that inositol trisphosphate receptor was phosphorylated by calmodulin-dependent kinase II in vivo. The extent of phosphorylation was enhanced by a type I phosphatase inhibitor, calyculin A. Two protein kinase C inhibitors, staurosporin and calphostin C, were found to behave atypically. Staurosporin seemed to stay in the plasma membrane without entering the cytoplasm, whereas calphostin C mimicked thapsigargin in depleting calcium stores.